Stents may be inserted into an anatomical vessel or duct for various purposes. Stents are often used to maintain or restore patency in a formerly blocked or constricted passageway, for example, following a balloon angioplasty procedure. Some stents may be used in conjunction with a suitable coating to form a coated stent, for example, to treat an aneurysm or to deliver therapeutic agents disposed on the stent or coating in close proximity to a target site.
Stents may be either self-expanding or balloon-expandable, or they can have characteristics of both types of stents. Self-expanding stents may be delivered to a target site in a compressed configuration and subsequently expanded by removing a delivery sheath, removing trigger wires and/or releasing diameter-reducing ties. In a stent made of a shape-memory alloy such as nitinol, the shape-memory alloy may be employed to cause the stent to return to a predetermined configuration upon removal of the sheath or other device maintaining the stent in its predeployment configuration.
With balloon-expandable stents, the stent may be delivered and deployed using a catheter and one or more balloons disposed on the catheter. The stent may be coupled to the balloon during insertion until the target site is reached, and then deployed by inflating the balloon to expand the stent to bring the stent into engagement with the target site. Alternatively, the stent may be placed separately in the vessel and a subsequent catheter having an expansion portion may then be inserted into the stent to expand the stent at the target site.
When stents are used in conjunction with a coating, gaps may be formed between the stent and the coating. To reduce the formation of gaps, a coated stent typically comprises a first coating disposed internal to the stent and a second coating disposed external to the stent. Therefore, the stent is sandwiched between the first and second coatings to reduce or eliminate gap formation.
However, where first and second coatings are used, the profile of the stent is increased by at least one additional layer, which may make it difficult to use the stent in smaller vessels or ducts. Moreover, if first and second coatings are employed, it may increase the deployment forced needed to deploy the stent.
In view of the above, it would be desirable to provide a coated stent having few or no gaps formed between the stent and the coating, having a reduced profile, and which facilitates a reduction in deployment force.